Fair point, but I assumed you were selling coins of reasonable value so postage of three bucks wouldn't be an issue. Anything of value less than UK £20 I don't do tracked and signed, I just do standard mail, which here in the UK is £3.10 for a small parcel and £1.15 for a padded envelope. I have never had any resistance to these prices even for items I list for just £3.00, but this is also the minimum I would ever list an item for because it just isn't worth the effort otherwise. I do sometimes do multiple item sales but these tend not to be as popular as single items.
With my listing I never include P&P in my listing price, I always have it separately. There are two reasons for this. (1) your listing price is more attractive, and (2) I offer combined postage so it makes sense to keep the postage separate. I also only ever charge the actual cost of postage plus eBay's fees on the postage i.e. postage x 1.1115
I have never had someone try to dupe me and return a different item. In fact I have never had someone try and return a coin I have listed. I always tick the listing condition 'used' and 'returns not accepted' also. In these cases a buyer can't return the item unless it's not as described or faulty and if you list your items correctly with good photos a buyer can't return them. Also unless a coin has never been circulated it will always have some mark on it which will show up in a good photo so that makes it very hard for someone to try and dupe you.
All I can say is I have never had a problem, but as with any marketplace there are always risks. I wouldn't dream of encouraging you to do something you are not confident about. It has to be your choice.
